U.S. patent number 5,377,266 [Application Number 08/089,522] was granted by the patent office on 1994-12-27 for scramble apparatus and descramble apparatus.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Toshihide Akiyama, Susumu Ibaraki, Noboru Katta, Hiroki Murakami, Seiji Nakamura, Hiroshi Takeno.
United States Patent |
5,377,266 |
Katta , et al. |
December 27, 1994 |
Scramble apparatus and descramble apparatus
Abstract
A scramble apparatus is for scrambling data including a variable
length code and a descramble apparatus for descrambling a scrambled
signal, and a scramble transmission apparatus comprising the
scramble apparatus and the descramble apparatus. A specific code of
data is converted into a readable code having a length equal to
that of an original code.
Inventors: |
Katta; Noboru (Itami,
JP), Murakami; Hiroki (Osaka, JP), Ibaraki;
Susumu (Toyonaka, JP), Nakamura; Seiji (Toyonaka,
JP), Akiyama; Toshihide (Takatsuki, JP),
Takeno; Hiroshi (Kyoto, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JP)
|
Family
ID: |
27525186 |
Appl.
No.: |
08/089,522 |
Filed: |
July 21, 1993 |
Foreign Application Priority Data
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Jul 21, 1992 [JP] |
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4-193742 |
Jul 27, 1992 [JP] |
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4-199392 |
Sep 29, 1992 [JP] |
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4-259540 |
Apr 13, 1993 [JP] |
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5-085929 |
Apr 13, 1993 [JP] |
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5-085930 |
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Current U.S.
Class: |
380/217;
348/416.1; 375/E7.226; 375/E7.231; 375/E7.144; 348/E7.056 |
Current CPC
Class: |
H04N
7/1675 (20130101); H04N 19/60 (20141101); H04N
19/91 (20141101); H04N 19/13 (20141101) |
Current International
Class: |
H04N
7/26 (20060101); H04N 7/30 (20060101); H04N
7/167 (20060101); H04L 009/00 () |
Field of
Search: |
;380/14,18,20,49 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0094254A3 |
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May 1983 |
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EP |
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0514663A2 |
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Apr 1992 |
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EP |
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57-207960 |
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Dec 1982 |
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JP |
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2096982 |
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Apr 1990 |
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JP |
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4082435 |
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Mar 1992 |
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JP |
|
4192779 |
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Jul 1992 |
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JP |
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4306096 |
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Oct 1992 |
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JP |
|
Other References
"A Scrambling System -M- for Communication Satellite Television",
Nezu et al., ITEJ Technical Report, vol. 15, No. 14, Feb. 1991, pp.
1-6..
|
Primary Examiner: Cangialosi; Salvatore
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Claims
What is claimed is:
1. A scramble transmission apparatus comprising a scramble
apparatus for scrambling compression image data and a descramble
apparatus for restoring a scramble signal generated by the scramble
apparatus to a signal not scrambled, wherein said scramble
apparatus selects at least one of coded parameters of:
(i) a motion vector obtained by predictive-coding the image data
with the motion of the vector compensated,
(ii) a coding block pattern signal indicating whether each coded
block contained in a block group has been coded, or not, in which
said block group in an image data is defined by plural coded blocks
and each coded block defined by plural pixel data,
(iii) a two-dimensional Huffman code of DCT coefficient which has
been coded by two-dimensional Huffman method using run and level
obtained by a predetermined scanning along the coefficients aligned
in two orthogonal directions as a result of prediction-applied DCT
conversion;
(iv) a DC component of DCT coefficients obtained after said
prediction-applied DCT conversion; and
(v) a code indicating how the image data has been quantized in
coding;
and wherein said scrambled apparatus includes a conversion
processing device for scrambling the selected parameters; and the
descramble apparatus performs a conversion inverse to the
conversion performed by the scramble apparatus.
2. A scramble apparatus comprising a conversion processing device
which selects at least one of coded parameters of:
(i) a motion vector obtained by predictive-coding the image data
with the motion of the vector compensated,
(ii) a coding block pattern signal indicating whether each coded
block contained in a block group has been coded, or not, in which
said block group in an image data is defined by plural coded blocks
and each coded block defined by plural pixel data,
(iii) a two-dimensional Huffman code of DCT coefficient which has
been coded by two-dimensional Huffman method using run and level
obtained by a predetermined scanning along the coefficients aligned
in two orthogonal directions as a result of prediction-applied DCT
conversion;
(iv) a DC component of DCT coefficients obtained after said
prediction-applied DCT conversion; and
(v) a code indicating how the image data has been quantized in
coding;
and said conversion processing device for scrambling the selected
parameters.
3. A scramble apparatus as defined in claim 2, wherein a motion
vector of the image data obtained by predictive-coding the image
data with the motion of the vector compensated is selected as a
parameter to be scrambled.
4. A scramble apparatus as defined in claim 3, wherein the
conversion processing device comprises a bit-inversion device for
bit-inverting a sign bit of the motion vector of the image
data.
5. A scramble apparatus as defined in claim 2, wherein the
conversion processing device obtains one coded block from data of a
plurality of pixels; selects, as a parameter to be scrambled, a
coding block pattern signal indicating whether each coded block
contained in a block group has been coded, or not, in which said
block group in an image data is defined by plural coded blocks and
each coded block defined by plural pixel data; and converts the
selected parameter into the coded block pattern signal indicating
the case in which the number of coded blocks is equal to that of
blocks coded in each block group indicated by the selected coded
block pattern signal.
6. A scramble apparatus as defined in claim 5, wherein the
conversion processing device is further for converting a selected
code, which is selected as a parameter for scrambling, and coded
according to the MPEG standard, to another code such that the
number of "1s" contained in the "cbp" of the another code is the
same as the number of "1s" contained in the "cbp" of the selected
code.
7. A scramble apparatus as defined in claim 2, wherein the
conversion processing device is further for selecting a
two-dimensional Huffman code of DCT coefficient which has been
coded by two-dimensional Huffman method using run and level
obtained by a predetermined scanning along the coefficients aligned
in two orthogonal directions as a result of prediction-applied DCT
conversion; and inverting a sign bit indicating the sign of the
selected code from positive to negative and vice versa.
8. A scramble apparatus as defined in claim 2, wherein the
conversion processing device is further for selecting, as a
parameter to be scrambled, a "dct.sub.-- dc.sub.-- differential"
signal of the image data; and scrambling the selected
parameter.
9. A scramble apparatus as defined in claim 2, wherein the
conversion processing device is further for selecting the code
indicating how the image data has been quantized in coding the
image data as a parameter to be scrambled; and scrambling the
selected parameter.
10. A scramble apparatus as defined in claim 9, wherein the
conversion processing device is further for selecting, as a
parameter to be scrambled, a quantization scale included in the
image data; and scrambling the selected parameter.
11. A descramble apparatus comprising an inverse conversion device
performing an inverse conversion which selects at least one of
coded parameters of:
(i) a motion vector obtained by predictive-coding the image data
with the motion of the vector compensated,
(ii) a coding block pattern signal indicating whether each coded
block contained in a block group has been coded, or not, in which
said block group in an image data is defined by plural coded blocks
and each coded block defined by plural pixel data,
(iii) a two-dimensional Huffman code of DCT coefficient which has
been coded by two-dimensional Huffman method using run and level
obtained by a predetermined scanning along the coefficients aligned
in two orthogonal directions as a result of prediction-applied DCT
conversion;
(iv) a DC component of DCT coefficients obtained after said
prediction-applied DCT conversion; and
(v) a code indicating how the image data has been quantized in
coding;
and descrambles the selected parameter.
12. A descramble apparatus as defined in claim 11, wherein inputted
data is a two-dimensional Huffman code of DCT coefficient which has
been coded by two-dimensional Huffman method using run and level
obtained by a predetermined scanning along the coefficients aligned
in two orthogonal directions as a result of prediction-applied DCT
conversion; and inverting a sine bit indicating positive and
negative of the level of the selected code.
13. A descramble apparatus as defined in claim 11, wherein inputted
data is obtained by selecting as a parameter to be scrambled, a
"dct.sub.-- dc.sub.-- differential" signal of the image data and
scrambling the selected parameter.
14. A descramble apparatus as defined in claim 11, wherein inputted
data is obtained by selecting the code indicating how the image
data has been quantized in coding the image data as a parameter to
be scrambled and scrambling the selected parameter.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a scramble apparatus and a
descramble apparatus which can be used by persons of limited skill
in scrambling and decoding operations which are required to
transmit or preserve digital-coded signals, and more particularly,
to a scramble apparatus which effectively controls the degree of
scramble according to purpose and a descramble apparatus for
reproducing a scrambled signal and to a scramble transmission
apparatus comprising the scramble apparatus and the descramble
apparatus.
2. Description of the Prior Arts
Conventional effective control scramble is used in TV broadcasting.
Regarding a scramble apparatus for handling a digital signal, sound
signal scramble is described in Television Institution Technical
Report Vol. 15, No. 14, pp.1-6.
The conventional scramble apparatus comprises an exclusive OR
calculation device for applying random numbers to an inputted
signal; a random number generator for generating a series of random
numbers by using a scramble key; and a control circuit, disposed
between the random number generator and the exclusive OR
calculation device, for controlling the random number to be applied
to an inputted signal.
In the construction of the conventional scramble apparatus, the
exclusive OR calculation device performs an logical exclusive OR of
the inputted signal by using a series of pseudo random numbers
generated by the random number generator. In this manner, the
inputted signal is bit-inverted. The control circuit controls the
bit inversion rate of inputted signals by appropriately switching
the application of the random numbers to the inputted signals. In
performing decoding, the exclusive OR calculation device performs
an logical exclusive OR of a scrambled signal by using the random
numbers generated by the random number generator. The pseudo random
number generated by the random number generator is determined by
the scramble key and decoding can be accomplished by only persons
having the scramble key.
In the above-described conventional scramble apparatus and an
apparatus for reproducing the scrambled signal, when the inputted
signal has been fixed length-coded, the position of each code and
the code length thereof are known if a bit of data is inverted at
random. Therefore, a code to which random numbers have not been
applied is correctly reproduced and the degree in which a person
not having the scramble key can reproduce the scrambled signal can
be controlled by a random number-applying rate.
The above-described conventional scramble apparatus has the
following problem: When an inputted signal includes a variable
length code, even a variable length-coded portion is converted into
a random bit pattern by scramble processing. This is because the
signal is bit-inverted at random. In the variable length-coded
code, the length of the code is not constant and all bit patterns
which can be expressed by each code length do not exist in a code
book. When several bits of the code are inverted, the code becomes
an unproducible code because the code is not provided in the code
book or is interpreted as a code having a different code length
from the original code. As a result, the start position of the
following code is erroneously found and subsequent data cannot be
reproduced.
Another disadvantage of the conventional scramble apparatus is that
in the case of compression-coded data, the data is often coded in
several parameters and the degree of influence is different
depending on the particular parameter used when the data is
extension-processed. Thus, when the data is scrambled at random,
control cannot be favorably accomplished.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a scramble
apparatus for effectively controlling an inputted signal including
a variable length code, a descramble apparatus for restoring a
scramble signal to an original signal, and a scramble transmission
apparatus comprising the scramble apparatus and the descramble
apparatus.
It is another object of the present invention to provide a scramble
apparatus for effectively controlling compression-coded data, a
descramble apparatus, and a scramble transmission apparatus
comprising the scramble apparatus and the descramble apparatus.
In accomplishing these and other objects of the present invention,
a scramble apparatus converts the code of an inputted signal
including variable length codes into a readable code having a
length equal to that of an original code.
According to the above construction, the quantity of scrambled data
is equal to that of original data. When the scrambled data is
reproduced without performing descramble, only a converted code is
reproduced in an erroneous value and other codes are not affected
by the conversion. That is, only a particular code is erroneously
reproduced without changing the quantity of the data.
A conversion device selects variable length codes, to be scrambled,
included in the data and converts each of the selected variable
length codes into a code, provided in a code book, having a length
equal to that of an original variable length code and indicating a
value different from that of the original variable length code.
According to the above construction, the converted code can be read
and there is no influence on other codes. A favorable control can
be accomplished without changing the quantity of the data.
A fixed length code is selected from variable length codes and
fixed length codes included in the data so as to scramble the
selected fixed length codes.
According to the above construction, a bit length is not
erroneously read after scramble is performed. That is, only the
data is reproduced erroneously.
The conversion device comprises a coder for coding original data
indicated by each code word, for converting the code word of each
code into a code word, provided in the code book, having a length
equal to that of the original code word and indicating a
significance different from that of the original code word; and a
packing device for arranging and reading coded codes, thus
generating a data sequence conforming to a rule.
According to the above construction, simultaneously with a signal
coding, scramble processing is executed. Therefore, compared with a
construction in which coding is performed and then a bit stream is
scrambled, the apparatus of the first embodiment eliminates the
provision of detector for detecting a code to be scrambled and can
generate a scramble signal efficiently.
According to the scramble apparatus of the present invention, the
following advantages are further observed.
(1) The predictive value of a predictive-coded image is made to
have an erroneous value. The predicted value corresponds to a
different position of the image. Therefore, an object of the image
looks as though it moves at random.
(2) When data is reproduced without performing descramble, each
block is reproduced at an erroneous position. Therefore, it looks
as if data arrangement was changed.
(3) In each block of DCT, the image can be controlled in the
frequency region of the image data by scrambling. A reproduced
image is blurred in its outline. In addition, an image formed by
predictive coding is influenced by a deteriorated predictive
value.
(4) The DC component of an image is scrambled and thus luminance
and hue of the image can be greatly deteriorated. In addition, a
great scramble effect can be obtained in a predictive-coded portion
of the image. Furthest, in the fixed length code of the data in
conformity to MPEG standard, scrambling can be accomplished without
other codes being affected by applying random numbers.
(5) Although the quality of an image itself is not deteriorated
greatly, the level of the luminance and hue of the image is
deteriorated. In addition, the quantization level is not uniform in
the entire image. In the case of data, such as a coded block, which
is altered for each portion of the image, quantization level is
discontinuous each time it is updated.
There is provided a descramble apparatus comprising an inverse
conversion device performing an inverse conversion. Thus,
reproduction can be accomplished by descrambling a scrambled
signal.
The present invention comprises the scramble apparatus and the
descramble apparatus.
According to the above construction, data can be correctly
transmitted between an admitted sending person and an admitted
receiving person. In the case of unadmitted receiver, data
transmission can be appropriately controlled.
A descramble apparatus comprising a descramble decoding device
receives a scramble signal obtained by converting a part or all
codes of data including variable length codes into different codes
each having a length equal to that of an original code and
indicating a value different from that of the original code; and
performs decoding processing or descramble processing and decoding
processing.
According to the above construction, the descramble processing and
the decoding processing of each code are performed by reading data
once whereas in the conventional apparatus, the descramble
processing and the decoding processing of each code are performed
separately, i.e., a device for the descramble processing and a
device for the decoding processing are required. Thus, the present
invention provides a compact circuit.
The descramble decoding device comprises a decoder for decoding
each code of inputted data and a code conversion device, wherein
the decoder decodes each code of inputted data similarly to a
signal not scrambled; and the code conversion device descrambles a
scrambled signal and converts the descrambled signal into the same
data as that generated by decoding each code.
According to the above construction, each code of the scramble
signal is decoded before descramble processing is executed.
Thereafter, each code is converted into the value of original data.
Thus, the decoding device of the present invention serves as a
reading device while in the conventional reproducing apparatus, a
detecting device for detecting a scrambled portion and the
reproducing device are required to read each code. Hence, the
present invention provides a compact circuit.
The descramble decoding device comprises a decoding detecting
device for detecting a scramble processing section based on the
decoding of each code included in inputted data and a decoded
result and an inverse conversion device for performing a conversion
inverse to scramble processing, wherein the decoding detecting
device detects a scrambled portion of inputted data; and the
inverse conversion device converts the detected portion into an
original data; and the converted data is inputted to the decoding
detecting device, whereby the converted data is decoded to obtain a
reproduced signal.
According to the above construction, the decoding detecting device
detects a scrambled portion and the descrambled signal is supplied
to the decoding detecting device based on a detected result so that
each code is decoded. That is, the decoding device of the present
invention serves as a reading device and hence, a compact circuit
can be manufactured. Further, the conversion processing inverse to
the conversion processing is performed before decoding operation is
carried out. Therefore, a simple construction can be provided.
A descramble apparatus as defined in claim 31, wherein the
descramble decoding device comprises the inverse conversion device
for performing a conversion inverse to scramble processing; and the
decoding detecting device which decodes a code which has released
from scramble or not been scrambled and detects a scrambled portion
of signals to be inputted based on a decoded result, wherein the
inverse conversion device descrambles the scrambled portion
detected by the decoding detecting device.
According to the above construction, since the scrambled portion is
detected based on a decoded signal, a compact circuit for detecting
the scrambled portion can be provided. It is unnecessary to refer
to a code book twice because the scrambled portion can be detected
based on the decoded signal.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of the present invention will
become clear from the following description taken in conjunction
with the preferred embodiments thereof with reference to the
accompanying drawings, in which:
FIG. 1 is a block diagram showing the construction of a scramble
apparatus and a descramble apparatus according to a first
embodiment of the present invention;
FIG. 2 is a view showing the outline of an image conforming to MPEG
standard;
FIG. 3 is an explanatory view showing the construction of a block
in a macroblock of a digital video signal in conformity to MPEG
standard;
FIG. 4 is an explanatory view showing a code book of a motion
vector used in MPEG standard;
FIG. 5 is an explanatory view showing a code book of a code block
pattern used in MPEG standard;
FIG. 6 is an explanatory view showing a code book of a coefficient
component of DCT (discrete cosine transform) used in MPEG
standard;
FIG. 7 is an explanatory view showing a code book of a motion
vector used in H.261;
FIG. 8 is a block diagram showing the construction of a scramble
apparatus according to a second embodiment of the present
invention;
FIG. 9 is a block diagram showing a signal processor according to
the second embodiment of the present invention;
FIG. 10 is a block diagram showing a bit inversion means provided
in a bit inversion device according to the second embodiment of the
present invention;
FIG. 11 is a block diagram showing the construction of a descramble
apparatus according to a third embodiment of the present
invention;
FIG. 12 is a block diagram showing the construction of a descramble
apparatus according to a fourth embodiment of the present
invention;
FIG. 13 is a block diagram showing the construction of a descramble
apparatus according to a fifth embodiment of the present
invention;
FIG. 14 is a block diagram showing the construction of a scramble
apparatus according to a sixth embodiment of the present invention;
and
FIG. 15 is an explanatory view showing an example of the
construction in which a conversion table is used in scramble
conversion.
DETAILED DESCRIPTION OF THE INVENTION
Before the description of the present invention proceeds, it is to
be noted that like parts are designated by like reference numerals
throughout the accompanying drawings.
FIG. 1 shows a scramble apparatus according to a first embodiment
of the present invention.
Referring to FIG. 1, the scramble apparatus comprises code
detectors 1 and 5 for reading a signal; random number generators 2
and 6; AND circuits 3 and 7; and exclusive OR circuits 4 and 8. A
conversion circuit 9 for performing a conversion of inputted data
comprises the random number generator 2, the AND circuit 3, and the
exclusive OR circuit 4. An inverse conversion circuit 10 comprises
the random number generator 6, the AND circuit 7, and the exclusive
OR circuit 8.
The operation of the scramble apparatus having the above-described
construction will be described below. An inputted signal is a video
signal in conformity to MPEG (Moving Picture Expert Group)
standard. MPEG standard is described in a specification and a draft
such as ISO/IEC IS 11172(1993), ISO-IEC/JCTI/SC29/WG11 NO328: Test
Model 3.
The outline of the video signal in conformity to MPEG is described
below with reference to FIG. 2. As shown in FIG. 2, data
construction comprises a sequence layer which indicates a motion
image. A header portion includes a sequence head-discriminating
signal serving as a start code, various kinds of parameters and
data, one or more groups of picture (GOP), and coding data of the
groups of picture (GOP).
The GOP layer comprising a frame of an arbitrary length includes
the head discriminating signal serving as the start code of the GOP
layer and coding data of one or more pictures. The picture layer
includes the head discriminating signal of a picture serving as the
start code of the picture and coding data of one or more slices.
The slice layer can include one or more arbitrary macroblock, the
head discriminating signal of the slice layer serving as the start
code of the slice layer, and the coding data of one or more
slices.
The macroblock is described below. The macroblock comprises a block
of luminance 16.times.16 pixel and a chrominance corresponding
thereto. Luminance (Y) and chrominance (Cb, Cr) are composed of
several smaller blocks of 8.times.8 pixel which is a fundamental
coding processing unit. FIG. 3 shows the structure of the
macroblock. The number of blocks of the macroblock is as follows:
When a signal to be processed is 4:2:0, the maximum number of
blocks is 6 (luminance: 4, chrominance: 2); when a signal to be
processed is 4:2:2, the maximum number of blocks is 8 (luminance:
4, chrominance: 4); when a signal to be processed is 4:4:4, the
maximum number of blocks is 12 (luminance: 4, chrominance: 8). The
data of each block is arranged in the order given in each block.
When it is unnecessary to send data to a block in predictive image
coding, for example, when a value obtained by quantizing an error
by the predictive image coding is all zero, the macroblock is
composed by skipping the block. That is, when a second block is
skipped in a signal of 4:2:1, five blocks of 1, 3, 4, 5, and 6 are
arranged to form the macroblock. When an n-th block is coded, the
block is indicated by bn=1 (n=1, 2, . . . ). When the n-th block is
not coded, the block is indicated by bn=0. A coded block pattern in
the macroblock is indicated by "coded block pattern". In the case
of the signal of 4:2:0, the signal is expressed by a binary number
of 6 bits of coded block pattern=(b1, b2, b3, b4, b5, b6). The
coded block pattern is coded in a variable length from 3 bits
through 9 bits depending on appearance frequency. In the case of
the signal of 4:2:2, the coded block pattern is expressed in a
binary number of 8 bits of coded block pattern=(b1, b2, b3, b4, b5,
b6, b7, b8).sub.2 and used as a code. In the case of the signal of
4:4:4, the coded block pattern is expressed in a binary number of
12 bits of coded block pattern=(b1, b2, b3, b4, b5, b6, b7, b8, b9,
b10, b11, b12).sub.2 and used as a code. The signal of 4:4:4 exists
in every macroblock. The macroblock includes blocks of predictive
type or coding type and motion vectors. Each block includes the
coding data of each discrete cosine transform (DCT) coefficient and
most of the macroblocks are variable length codes.
The code detector 1 has a code book used to reproduce each code in
order to read the content of all data of inputted bit string, thus
detecting which information an inputted bit indicates. In
particular, the code detector 1 detects a motion vector, a coded
block pattern, "dct.sub.-- dc.sub.-- differential" code,
"dct.sub.-- coef.sub.-- first", "dct.sub.-- coef.sub.-- next", and
"quantizer.sub.-- scale" code as the scramble point of the inputted
signal (bit). The scramble point is described below.
The motion vector exists in each macroblock to be frame-to-frame
predictive-coded. FIG. 4 is a code book showing the motion vector.
According to the code book, a difference signal indicating the
difference between a precedent motion vector and an actual motion
vector is coded. The actual motion vector is obtained by adding a
value read from the code book to the precedent motion vector.
As shown in FIG. 4, codes at positions symmetrical with respect to
0, namely, a positive code word and a negative code word obtained
by inverting the positive code word are different from each other
at the last one bit while the remaining bits thereof are equal to
each other.
The code detector 1 detects the last bit of the motion vector as a
scramble point except the case where the value of the motion vector
is zero.
With regard to a signal of "coded block pattern", the last bit of a
code is detected as a scramble point supposing that a signal to be
processed is a signal of 4:2:0. In the case of "111", "01011",
"01010", "01001", and "01000", the last bit of a code is not
scrambled and thus not detected. FIG. 5 is a code book of coded
block pattern used in the case where a signal is 4:2:0. As apparent
from FIG. 5, except when a code is "111", all codes and codes
obtained by inverting the last bit thereof exist in the code book.
The numbers of "1" are equal to each other in all codes except the
codes of "01011", "01010", "01001", and "01000" when the values of
coded block pattern indicated by the codes are expressed by a
binary number. Thus, an inputted signal is converted into a signal
having a code length equal thereto, with a decoded position being
erroneous in reproducing an original signal from the converted
signal. For example, when the code of coded block pattern is
converted from "1101" into "1100", a signal of a fourth block is
reproduced as a signal of a third block.
The coefficient component of DCT is coded by using two-dimensional
Huffman coding. That is, the combination of consecutive number
(run) of zeros and a value (level), except zero, which follows the
run is used to perform a scan according to a predetermined method
after quantization is performed. FIG. 6 shows a part of the code
book. Reference symbol (s) indicates a positive code or a negative
code of the level. That is, a positive level indicates 0 and a
negative level indicates 1. Accordingly, when the last bit of a
detected code word is inverted, the inverted cord word exists in
the code book, with the code of the level thereof inverted. Thus,
regarding the coefficient component of DCT, the code detector 1
detects the two-dimensional code word of Huffman code as a scramble
point.
Quantization scale exits as a 5-bit signal at a position
immediately after the signal for discriminating the head of slice.
The quantization scale exits as a 5-bit signal in the macroblock in
altering the quantization scale of the macroblock in the slice.
Since all 5-bit patterns correspond to the value of the
quantization scale except the case where a 5-bit pattern has only
zeros, even though a 5-bit signal is converted into any other 5-bit
signals, a signal indicating a different value is generated. The
code detector 1 detects the quantization scale as a scramble point
when a currently inputted bit is a signal of the quantization
scale.
A scramble mode signal to be inputted to the code detector 1 is a
5-bit signal indicating a motion vector, a coded block pattern, a
DCT coefficient component, a DC component of DCT, and whether or
not the quantization scale is scrambled. When each bit is "1", the
quantization scale is scrambled while when each bit is "0",
quantization scale is not scrambled. The combination of scramble
mode is indicated by setting a plurality of bits to "1". The code
detector 1 outputs a signal instructing the execution of scramble
to the AND circuit 3 and the random number generator 2 when a
scramble point is detected with the bit of the scramble instruction
signal indicating "1".
In response to one scramble instruction signal, which is a one-bit
pulse signal, the random number generator 2 generates a 1-bit
random number in accordance with a rule determined by a scramble
key, thus outputting the generated random number to the AND circuit
3. Therefore, when the instruction signal of five sequential bits
are produced, random number generator 2 also generates five
sequential bits of random numbers in response to the five
sequential bits of the instruction signal. It is noted that the
random number generator 2 generates random numbers at a bit rate
equal to the bit rate of the input signal. Thus, the scrambling
effected at the exclusive OR circuit 4 is carried out at every bit
during which the AND circuit 3 is maintained opend by a HIGH level
signal supplied thereto from the code detecting apparatus 1.
The AND circuit 3 allows the output of the random number generator
2 to pass therethrough only when the AND circuit 3 receives the
scramble instruction signal from the code detector 1, thus
outputting it to the exclusive OR circuit 4 so that the output of
the AND circuit 3 is scrambled.
The receiving side having the same construction as the scramble
apparatus descrambles a scramble signal. The function of the code
detector 5 is identical to that of the code detector 1. In response
to the scramble mode signal, the detector 5 outputs the scramble
instruction signal to the random number generator 6 and the AND
circuit 7. In this case, since the scramble signal maintains the
grammar of MPEG even after the scramble is performed, the scramble
instruction signal is capable of indicating the bit used at the
time of the execution of the scramble. The function of the random
number generator 6 is identical to that of the random number
generator 2. Therefore, in response to the scramble key, the random
number generator 6 generates the same random number as that
generated in the execution of the scramble, thus outputting the
generated random number to the AND circuit 7. In response to the
output of the AND circuit 7, the exclusive OR circuit 8 applies the
same random number as that used in the execution of the scramble to
the scramble signal. In this manner, descramble processing is
executed.
As described above, in the first embodiment, random numbers are
added to the scramble signal with the last bit of the motion vector
signal set as the scramble point. The scramble according to the
first embodiment effectively deteriorates the quality of an image
in a portion in which a projected image moves in a great amount.
Since the scramble is performed in a code block pattern, a scramble
image is obtained with a reproduction position located erroneously
when the descramble processing is not performed. In addition,
random numbers are added,to the last bit of the Huffman code of the
DCT coefficient. As a result, the positive and negative signs of an
error in predictive coding become random. Consequently, an image is
obtained with the information of detailed portion thereof
deteriorated. Luminance and hue of the DC component of DCT
coefficient can be greatly deteriorated. The luminance level of an
image can be effectively made to be random owing to the scramble of
quantization scale. In the first embodiment, the code detector 1
detects of all of these scramble positions, and the scramble
processing is switched by the scramble mode signal. In this manner,
the scramble apparatus is capable of performing all scrambles and
achieving the combination of each scramble.
In the first embodiment, an image data in conformity to MPEG
standard is used, but it is possible to scramble data coded by
other methods provided that a variable length code is used. FIG. 7
shows a code book of a motion vector code used in an advice plan
H.261 of CCIR. Similarly to the first embodiment, in the case of
the motion vector of H.261, the last bit of the motion vector can
be detected as a scramble point with a similar effect.
A scramble apparatus according to a second embodiment of the
present invention is described below with reference to FIGS. 8
through 10. FIG. 8 shows the construction of the scramble apparatus
according to the second embodiment.
Referring to FIG. 8, the scramble apparatus comprises a signal
processing device 11 for converting a video signal such as DCT or a
predictive processing into a parameter to be coded and quantizing a
necessary video signal; a coder 12 for coding each parameter
generated by the signal processing device 11; a bit inversion
circuit 13 for performing an logical exclusive OR of a bit to be
scrambled for each parameter by using a series of random numbers
generated by a random number generator 14; and a packing device 15
for arranging coded data in a predetermined order, thus outputting
the arranged data as a bit stream.
The operation of the scramble apparatus having the above-described
construction is described below. Similarly to the first embodiment,
the scramble apparatus generates a scramble signal for a signal
conforming to MPEG standard. A signal is inputted to the signal
processing device 11 of the scramble apparatus.
FIG. 9 is a block diagram showing processing to be executed in the
signal processing device 11. Referring to FIG. 9, the signal
processing device 11 comprises a DCT processing block 16; a
quantization processing block 17; an inverse quantization
processing block 18; an inverse DCT processing block 19; a frame
memory 20; frame-to-frame predictive/unpredictive block 21; and a
motion detecting block 22. In the coding according to MPEG
standard, the signal processing device 11 comprises three frames,
namely, an intra-coded picture (I) frame for performing a coding in
a frame, a predictive-coded picture (P) frame for performing a
forward predictive coding based on a past frame, and a
bidirectionally predictive-coded picture (B) frame for performing a
predictive coding in combination of the forward predictive coding
and a backward predictive coding based on a future frame.
In the (I) frame, an inputted signal is processed by the DCT
processing block 16, quantized by the quantization processing block
17, and then sent to the coder 12. In the (P) frame, a quantized
past frame is processed for reproduction by the dequantization
processing block 18 and the inverse DCT processing block 19. If the
signal is a prediction-difference signal, a predictive signal is
added to the prediction-difference signal. The result obtained by
the addition is stored in the frame memory 20. A motion is detected
by the motion detecting block 22 based on a current frame. The
predictive signal is generated by the frame-to-frame
predictive/unpredictive block 21 based on the motion vector and a
signal of the frame memory 20. A difference value between the
predictive signal and the current frame is processed by the DCT
processing block 16 and the quantization processing block 17.
In the (B) frame, the current frame is predicted based on not only
the past frame used by the (P) frame but also on the future frame.
Then, both predictions are synthesized to generate a predictive
frame so as to perform a predictive coding similarly to the (P)
frame. Thus, the signal processing device 11 outputs to the coder
12 data necessary for determining whether or not it is necessary to
perform the weighting of quantized coefficient components and
quantization, motion vector, predictive coding and the like. The
coder 12 comprises coding blocks for coding data and the bit
inversion circuit 13. Each data is inputted to a corresponding
coding block for coding and each data coded in the order based on
MPEG standard is transmitted to the packing device 15. The bit
inversion circuit 13 is provided for a coding block which codes
data to be scrambled.
The bit inversion circuit 13 is composed of a subcircuit, shown in
FIG. 10, provided on each coding block which codes data to be
scrambled.
Referring to FIG. 10, reference numerals 23 through 33 denote
exclusive OR circuits. Reference numerals 34 through 44 denote AND
circuits. A bus for transmitting data from each coding block to the
packing device 15 comprises 32 bits. Exclusive OR circuits 23
through 33 are provided in the lower 11 bits of 32 bits so that a
signal rn0 through rn10 outputted from the random number generator
12 can be applied to the bit inversion circuit 13. Data to be
scrambled includes motion vector, Huffman coding of DCT
coefficient, "dct.sub.-- dc.sub.-- differential" signal which is a
difference signal of DC component of DCT, and quantization scale.
Data sent from the coding block is sequentially applied to the bus
from a lower bit. A signal outputted from the random number
generator 14 is controlled for each bit by the AND circuits 34
through 44 and the inputs cont0 through cont10 supplied
thereto.
In the case of a coding block of a motion vector, only a cont0
signal of a bit corresponding to the last bit is "1". In the case
of a coding block which generates a Huffman code of DCT
coefficient, only a signal of cont0 of cont0 through cont10 is "1"
and other signals are "0" in performing scramble.
In the case of a signal of "dct.sub.-- dc.sub.-- differential", the
bit number same as the bit length of the signal "dct.sub.--
dc.sub.-- differential" is "1" and based on a decoded result of a
code, indicating a code length, existing immediately before the
signal "dct.sub.-- dc.sub.-- differential", switching of cont0
through cont10 is effected. In a coding block of quantization
scale, cont0 through cont4 are "1". Therefore, a code to be
scrambled is bit-inverted by a random number generated by the
random number generator 14. A random number is added to the
scramble signal in such a manner that the order generated by the
random number generator 14 is equal to the appearing order of a
code to which the random number has been added in a bit stream
conversion. Cont0 through cont 10 are inputted by finding cont0
through cont 10 for each coding block based on scramble mode.
Each code scrambled as above is sent to the packing device 15 under
the control of the coder 12. The packing device 15 connects the
codes to each other in the order of the code in conformity to MPEG
standard, thus outputting the connected codes as a bit stream.
As described above, in the second embodiment, simultaneously with a
signal coding, scramble processing is executed. Therefore, compared
with a construction in which coding is performed and then a bit
stream is scrambled, the apparatus of the first embodiment
eliminates the provision of detector for detecting a code to be
scrambled and can generate a scramble signal efficiently.
In the second embodiment, in the coding block, simultaneously with
a signal coding, scramble processing is executed. But if there are
a small number of patterns, for example, motion vectors to be
scrambled, a table for coding scrambled data and a table for coding
data not scrambled may be prepared. In this case, a selective
control can be made by using a random number.
A descramble apparatus according to the third embodiment of the
present invention is described below with reference to FIG. 11
showing the construction thereof. The scramble signal generated by
the scramble apparatus according to the second embodiment is
inputted to the descramble apparatus. The descramble apparatus
comprises a decoder 45 for decoding each code of an inputted
signal; a conversion processor 46 for converting decoded data into
a correct reproduction signal; a buffer 47; a control circuit 48
for controlling an output of the buffer 47 and controlling the
decoder 45 by distinguishing the kind of a signal and selecting a
table appropriate for decoding; a random number generator 49 for
generating random numbers based on the scramble key and controlling
the conversion processor 46 based on the output thereof; and an
image reproducing device 50.
The operation of the scramble apparatus having the above-described
construction is described below. The buffer 47 outputs a signal
inputted thereto to the decoder 45 according to a signal of the
control circuit 48. The decoder 45, comprising a decoding
processing section for decoding each code of a video signal and a
code book table, alters the content of the code table according to
a table select signal transmitted from the control circuit 48 and
decodes a received signal with reference to the code book table,
thus outputting the decoded value to the control circuit 48 and the
conversion processor 46 and outputting a code length signal to the
control circuit 48. In response to the decoded value and the code
length signal outputted from the decoder 45, the control circuit 48
outputs a decoded code length signal to the buffer 47 and shifts
the decoded code length signal by the bit number of the decoded
code length signal so as to allow the decoder 45 to receive a
signal. In addition, the control circuit 48 recognizes a signal
which will be inputted thereto based on the rule of a series of
signals in conformity to MPEG standard as well as obtained decoded
result, thus outputting a select signal indicating a code to be
decoded by the decoder 45 to the decoder 47. In this manner, the
control circuit 48 makes a control so that a correct table can be
used in decoding. In addition, the control circuit 48 outputs the
information of a decoded signal to the conversion processor 46. In
response to the output of the control circuit 48 and the scramble
mode signal, the conversion processor 46 discriminates whether or
not data should be scrambled. The conversion processor 46 performs
a conversion of a code to be scrambled in response to the output of
the random number generator 49 by using the scramble key, thus
outputting the result to the image reproducing device 50. If data
received by the conversion processor 46 should not be scrambled,
the conversion processor 46 outputs it to the image reproducing
device 50 without decoding it. Regarding the processing of motion
vector to be performed in the conversion processor 46, when the
output of the random number generator 49 is 1, a decoded value of x
is inverted into -x as shown in the code book of FIG. 4. When the
output of the random number generator 49 is 0, processing is not
performed. Regarding the processing of two-dimensional Huffman code
of DCT coefficient, when the output of the random number generator
49 is 1, the code of a value of a decoded level is inverted. When
the output of the random number generator 49 is 0, processing is
not performed. In the case of "dct.sub.-- dc.sub.-- differential"
signal and the quantization scale, a random number is applied to
all bits. In this manner, based on data decoded and descrambled,
the image reproducing apparatus 50 reproduces an image.
As described above, the control circuit of a normal reproducing
device not scrambled has a function of detecting the scramble
processing section and descramble processing is performed by the
reproducing section. Unlike the conventional apparatus in which
both descramble processing section and data reproducing section
required a code book for reading a variable length code of data,
the decoder 45 of the reproducing section of the apparatus
according to the present invention is capable of performing
descramble processsing and the reading of the variable length code
of data. Therefore, descramble processing can be executed by a
compact circuit.
A descramble apparatus according to the fourth embodiment of the
present invention is described below with reference to FIG. 12. The
descramble apparatus comprises a buffer 51 for storing an inputted
signal temporarily; a shifter 52 for shifting the received signal
by the processed number of bit, thus outputting the result to an
exclusive OR circuit 57; a random number generator 53 for
generating a series of random numbers identical to that used in
scramble; a decoder 54 for decoding each code of an inputted
signal; a control circuit 55 for controlling the respective devices
based on a value decoded by the decoder 54; an image reproducing
device 56; and the exclusive OR circuit 57.
The operation of the descramble apparatus having the
above-described construction is described below. An inputted signal
is the same as that of the third embodiment. The inputted signal is
stored in the buffer 51 which outputs a predetermined number of
bits to the shifter 52 each time the buffer 51 receives a request
signal from the shifter 52. The shifter 52 shifts the inputted
signal according to an instruction sent from the control circuit 55
and outputs constant bits in parallel with a bit to be decoded next
at the head thereof to the exclusive OR circuit 57. When the number
of bits stored in the shifter 52 becomes less than a predetermined
bit, the shifter 52 outputs a request signal to the buffer 51. The
output of the shifter 52 passes through the exclusive OR circuit 57
without being processed and inputted to the decoder 54. The decoder
54 comprises a decoding processing section and a code book. That
is, the decoder 54 performs decoding by appropriately selecting an
inputted code book and a decoding processing based on a select
signal sent from the control circuit 55, thus outputting a decoded
value and a code length to the control circuit 55. In addition, the
decoder 54 outputs the bit information of a code to be scrambled to
the control circuit 55. The control circuit 55 outputs a decoded
value to the image reproducing device 56 if the decoded code is not
to be scrambled and outputs an instruction for the shift of the
code length of the decoded code to the shifter 52. If a decoded
code is to be scrambled, the control circuit 55 sends a control
signal to the random number generator 53 in response to the signal
outputted from the decoder 54 so that the exclusive OR circuit 57
performs an logical exclusive OR by using a series of random
numbers generated by the random number generator 53. At this time,
the control circuit 55 does not send a shift signal to the shifter
52 so that the same signal is outputted again from the shifter 52.
The signal outputted again from the shifter 52 is descrambled by
the exclusive OR circuit 57, correctly decoded by the decoder 54,
and outputted to the control circuit 55. The control circuit 55
transmits a correctly decoded signal to the image reproducing
device 56 and an instruction for shifting the code length of the
decoded signal to the shifter 52. The image reproducing device 56
executes a signal processing such as an inverse DCT based on a
decoded value supplied by the control circuit 55.
As described above, in the fourth embodiment, the decoder 54
decodes each code included in an inputted scramble signal and the
control circuit 55 detects a scrambled portion based on the result
produced by the decoder 54. Upon receipt of the detected result,
the random number generator 53 and the exclusive OR circuit 57
release the scramble and then, the decoder 54 decodes the received
code again. In this manner, the scramble signal is descrambled.
Accordingly, the number of decoding and that of code books are
small and in addition, descramble processing is performed before
each code is decoded. Thus, the apparatus of the fourth embodiment
executes the descramble processing faster than the third
embodiment.
A descramble apparatus according to the fifth embodiment of the
present invention is described below with reference to FIG. 13. The
descramble apparatus comprises a buffer 58 for storing an inputted
signal temporarily; a shifter 59 for shifting the received signal
by thee processed number of bit, thus outputting the result to an
exclusive OR circuit 57; a random number generator 60 for
generating a series of random numbers identical to those in
scramble; the exclusive OR circuit 61 for performing an logical
exclusive OR by using a series of random numbers generated by the
random number generator 60; a sign bit processor 62 for reproducing
a sign bit; a decoder 64 for decoding each code of an inputted
signal; a control circuit 55 for controlling the respective devices
based on inputted signals and outputting a decoded result; and an
image reproducing device 65 for reproducing an image based on the
result of decoding.
The operation of the descramble apparatus having the
above-described construction is described below. An inputted signal
is the same as that of the third embodiment. The inputted signal is
stored in the buffer 58 which outputs a predetermined number of
bits to the shifter 59 each time the buffer 51 receives a request
signal from the shifter 59. The shifter 59 shifts the inputted
signal according to an instruction sent from the control circuit 64
and outputs constant bits in parallel with a bit to be decoded next
at the head thereof to the exclusive OR circuit 61. When the number
of bits stored in the shifter 59 becomes less than a predetermined
bit, the shifter 59 outputs a request signal to the buffer 58.
Based on a decoded value and a signal indicating the code length
thereof supplied by the decoder 63, the control circuit 64 outputs
an instruction to the shifter 59 so that the bit length processed
by the shifter 59 is shifted. In addition, based on a signal
supplied by the decoder 63, the control circuit 64 detects a
scrambled portion, thus controlling the random number generator 60
and the sign bit processor 62. The control method to be performed
by the control circuit 64 is described below. Regarding "dct.sub.--
dc.sub.-- differential" signal, based on the decoding information
of "dct.sub.-- dc.sub.-- size.sub.-- luminance" signal or
dct.sub.-- dc.sub.-- size.sub.-- chrominance" signal indicating a
code length immediately before the "dct.sub.-- dc.sub.--
differential" signal, the control circuit 64 outputs a signal to
the random number generator 60 so that the exclusive OR circuit 61
performs an logical exclusive OR of signals sequentially from a
signal at the head of a series of signals to be outputted from the
shifter 59 according to the decoding information which indicates
bits necessary to be decoded. Regarding the quantization scale,
when it is recognized that bits of fixed length code are decoded
sequentially and quantization scale is inputted next, the random
number generator 60 is controlled so that random numbers are
applied to the calculation of the logical exclusive OR of the next
five bits. Regarding the coefficient component of DCT, the decoder
63 is provided with a code book for restoring the information of
bit patterns prior to a sign bit. The decoding signal indicating
the information of bit patterns is sent to the control circuit 64.
The control circuit 64 detects the next 1 bit as a sign bit and
allows the sign bit processor 62 to be operable and transmits a
control signal to the random number generator 60 and transmits
random numbers to the sign bit processor 62. Only when the random
number is "1", the sign bit processor 62 inverses the sign bit,
thus outputting the inverted sign bit to the decoder 63. The
decoder 63 generates a decoding signal based on the sign bit and
the value of a decoded portion, thus outputting the generated
decoding signal to the control circuit 64. In the case of the
motion vector, there is provided, in the decoder 63, a code book of
pattern in which the sign bit of a code indicating the value of
motion vector shown in FIG. 4 is excluded. The decoder 63 decodes
codes, thus sending the decoded values and the code lengths to the
control circuit 64. The control circuit 64 decides the following
one bit as a sign bit and allows the sign bit processor 62 to be
operable and sends a control signal to the random number generator
60. The random number generator 60 sends random numbers to the sign
bit processor 62. The sign bit processor 62 inverses a sign bit
only when the random number is "1", thus outputting the result to
the decoder 63. Then, the control circuit 64 outputs a control
signal to the shifter 59 so that a subsequent expansion code is
inputted to the decoder 63. Based on the decoded value and the
expansion code of the sign bit, the decoder 63 generates a correct
decoding signal, thus outputting the decoding signal to the control
circuit 64. The correctly decoded value is transmitted to the image
reproducing device 65. The control circuit 64 allows the decoder 63
to select the code book similarly to the first embodiment.
As described above, based on a previous code decoded by the decoder
63, the control circuit 64 detects a scrambled portion of a code to
be processed and the scramble is released and a reproduction is
effected by the random number generator 60, the exclusive OR
circuit 61, the sign bit processor 62. As a result, only one code
book for reading a variable length code is required in the decoder
63. Thus, similarly to the first and third embodiments, a compact
circuit is used. In addition, since it is unnecessary to refer to
the code book twice unlike the fourth embodiment, a high speed
processing can be accomplished. Further, since the code book used
in the decoder 63 does not require sign bit, it is unnecessary to
store a large number of memories.
A scramble apparatus according to the sixth embodiment of the
present invention is described below with reference to FIG. 14. The
scramble apparatus comprises a code detector 66 for distinguishing
inputted signals from each other and reading the bit number of a
signal; a control circuit 67 for determining whether or not the
current code of an inputted signal is scrambled, based on the
result detected by the code detector 66 and controlling ON and OFF
of the scramble; a signal change-over device 68 for switching
processings of inputted signals from each other based on the output
of the control circuit 67; a random number generator 69; a cyclic
shifter 70 for performing a cyclic shift according to the output of
the random number generator 69; and an exclusive OR circuit 71.
The operation of the scramble apparatus having the above-described
construction is described below. The code detector 66 has a
code-reproducing code book for reading the contents of all data of
inputted signals and detecting the information indicated by an
inputted bit, thus outputting the information to the control
circuit 67. When the coded block pattern signal is detected, the
control circuit 67 selects processing as a code to be scrambled
according to a signal supplied by the code detector 66 and controls
the signal change-over device 68, thus outputting a control signal
indicating the output of a random number necessary for scramble to
the random number generator 69. The method to be performed by the
control circuit 67 is described below.
When a code not to be scrambled is detected, the control circuit 67
allows the signal change-over device 68 to output a signal
indicating that an inputted signal is connected to a terminal (c),
and the inputted signal is outputted from the signal change-over
device 68 without being processed. When a "coded block pattern"
signal of inputted signals is detected, the control circuit 67
sends an instruction that the "coded block pattern" signal is
connected with a different terminal to the signal change-over
device 68 so as to scramble the signal is scrambled, thus
outputting an instruction to the random number generator 69 so that
the random number generator 69 generates random numbers. When a
signal to be processed is 4:2:0, the control circuit 67 outputs a
control signal to the signal change-over device 68 so that the
inputted signal is connected to the terminal (a). Then, the control
circuit 67 outputs the information of the code length of the signal
and an instruction of generating a random number of 1 bit to the
random number generator 69. In response to the output of the
control circuit 67, the random number generator 69 outputs the
random number of 1 bit to the exclusive OR circuit 71 by using the
scramble key so that the random number of 1 bit is applied to the
last bit of the code. In the case of "111", "01011", "01010",
"01001", and "01000", the code is not scrambled and the inputted
signal is connected with the terminal (c) of the signal change-over
device 68. When a signal to be processed is 4:2:2 or 4:4:4, the
control circuit 67 outputs a control signal to the signal
change-over device 68 so that the inputted signal is connected to
the terminal (b) of the signal change-over device 62 and in
addition, the control circuit 67 outputs an instruction to the
random number generator 69 so that the random number generator 69
generates a random number of four bits. The random number generator
69 generates the random number of four bits by using the scramble
key, thus transmitting the random number of four bits to the cyclic
shifter 70. The cyclic shifter 70 cyclically shifts the code of the
coded block pattern by the number of times indicated by the signal
outputted from the random number generator 69, thus outputting the
result. Similarly to the signal of 4:2:0, the length of the code is
equal to that of an original code and the position of each block is
converted into an erroneous position. The signal generated as above
is inserted into the code position of the original "coded block
pattern" and outputted from the scramble apparatus.
As described above, the codes of "111", "01011", "01010", "01001",
and "01000" are not processed in the case the signal of 4:2:0.
Random numbers are applied to the last bit of the remaining codes
for a code change in such a manner that the code length of a
scrambled signal is equal to that of a signal not scrambled and the
number of blocks remain unchanged. The cyclic shifter 70 cyclically
shifts the code of the coded block pattern in the case of the
signal 4:2:2 or 4:4:4. Thus, the number of "1" in the code remains
unchanged and hence signal processing can be accomplished easily.
Since the predictive coding is used in the coding method of MPEG
standard, the position of a block is moved in a reproduced signal
and a predictive error signal is added to a predicted value. Hence,
scramble processing can be effectively performed.
In the sixth embodiment, when a part of a variable length code word
is bit-inverted, random numbers are applied to a bit which
corresponds to a code word provided in the code book. But in
converting a code word into a code worn without changing the code
length, not only the conversion table may be utilized to replace
the entire code word with a different code word, but also any other
means may be employed. FIG. 15 shows an example of the construction
of an apparatus when a conversion table is used. The apparatus
comprises a conversion table 72; AND circuits 73 and 74; an
exclusive OR circuit 75; a NOT circuit 76; a random number
generator 77. In this construction, the random number generator 77
is controlled in deciding whether an inputted signal is converted
into a scramble signal or not processed.
In the sixth embodiment, data in conformity to MPEG standard is
inputted to the apparatus, but data including a variable length
word such as compression image data or a sound signal can be
handled. According to the present invention, not only a scrambled
parameter, but also data including a variable length word can be
scrambled without increasing the code length thereof. Since a
standardized operation has been continuously performed, scramble
can be accomplished in a similar method in standardized MPEG 1 and
MPEG 2 although the specification of MPEG standard may be altered
in some extent. Although data of a variable length code may be
altered in MPEG standard in future, scramble can be performed with
attention paid to each parameter.
Although the present invention has been fully described in
connection with the preferred embodiments thereof with reference to
the accompanying drawings, it is to be noted that various changes
and modifications are apparent to those skilled in the art. Such
changes and modifications are to be understood as included within
the scope of the present invention as defined by the appended
claims unless they depart therefrom.
* * * * *